Phase frequency detector with limited output pulse width and method thereof

Abstract

Phase frequency detectors with limited output pulse width and related methods are disclosed. The proposed phase frequency detector generates a first output signal and a second output signal corresponding to phase difference or frequency difference between a first signal and a second signal. When the phase difference between the first and second signals is greater than a predetermined delay, the pulse width of the first output signal is limited, so that the proposed phase frequency detector has a limited equivalent output pulse width.

1. A phase frequency detector comprising:
 a first edge detector for detecting first-type edges of a first signal to generate a first detection signal and for changing the level of the first detection signal according to a first control signal; 
 a first latch unit coupled to the first edge detector for latching the first detection signal to generate a first output signal and for changing the level of the first output signal according to a third control signal; 
 a first delay unit coupled to the first latching unit for delaying the first output signal to generate a first delayed signal; 
 a second edge detector for detecting the first-type edges of a second signal to generate a second detection signal and for changing the level of the second detection signal according to a second control signal; 
 a second latch unit coupled to the second edge detector for latching the second detection signal to generate a second output signal and for changing the level of the second output signal according to the third control signal; 
 a second delay unit coupled to the second latching unit for delaying the second output signal to generate a second delayed signal; 
 a combination logic coupled to the first and second latch units for performing a predetermined logical operation on the first output signal and the second output signal to generate the third control signal; 
 a first logic unit coupled to the first delay unit, the combination logic, and the first edge detector, for performing a first logical operation on the first delayed signal and the third control signal to generate the first control signal; and 
 a second logic unit coupled to the second delay unit, the combination logic, and the second edge detector, for performing a second logical operation on the second delayed signal and the third control signal to generate the second control signal. 
 
   
   
     2. The phase frequency detector of  claim 1 , wherein the first edge detector is a D-type flip-flop. 
   
   
     3. The phase frequency detector of  claim 2 , wherein the second edge detector is a D-type flip-flop. 
   
   
     4. The phase frequency detector of  claim 1 , wherein the first latch unit is a D-type flip-flop. 
   
   
     5. The phase frequency detector of  claim 4 , wherein the second latch unit is a D-type flip-flop. 
   
   
     6. The phase frequency detector of  claim 1 , wherein the first and second delay units apply the same delay on the first output signal and the second output signal, respectively. 
   
   
     7. The phase frequency detector of  claim 6 , wherein the first and second delay units are substantially the same. 
   
   
     8. The phase frequency detector of  claim 1 , wherein the first and second logical operations are substantially the same. 
   
   
     9. The phase frequency detector of  claim 1 , wherein the first edge detector sets the level of the first detection signal to a first predetermined level during the active period of the first control signal. 
   
   
     10. The phase frequency detector of  claim 9 , wherein the second edge detector sets the level of the second detection signal to the first predetermined level during the active period of the second control signal. 
   
   
     11. The phase frequency detector of  claim 1 , wherein the first latch unit sets the level of the first output signal to a first predetermined level during the active period of the third control signal. 
   
   
     12. The phase frequency detector of  claim 11 , wherein the second latch unit sets the level of the second output signal to the first predetermined level during the active period of the third control signal. 
   
   
     13. The phase frequency detector of  claim 1 , further comprises a delay setting unit coupled to at least one of the first delay unit and the second delay unit for programming the delay amount of the coupled delay unit. 
   
   
     14. A method for generating a first output signal and a second output signal corresponding to phase difference or frequency difference between a first signal and a second signal, the method comprising:
 detecting first-type edges of the first signal to generate a first detection signal; 
 changing the level of the first detection signal according to a first control signal; 
 latching the first detection signal to generate a first output signal; 
 changing the level of the first output signal according to a third control signal; 
 delaying the first output signal to generate a first delayed signal; 
 detecting the first-type edges of the second signal to generate a second detection signal; 
 changing the level of the second detection signal according to a second control signal; 
 latching the second detection signal to generate a second output signal; 
 changing the level of the second output signal according to the third control signal; 
 delaying the second output signal to generate a second delayed signal; 
 performing a predetermined logical operation on the first output signal and the second output signal to generate the third control signal; 
 performing a first logical operation on the first delayed signal and the third control signal to generate the first control signal; and 
 performing a second logical operation on the second delayed signal and the third control signal to generate the second control signal. 
 
   
   
     15. The method of  claim 14 , wherein the step of delaying the first output signal and the step of delaying the second output signal apply the same delay on the first output signal and the second output signal, respectively. 
   
   
     16. The method of  claim 14 , wherein the first and second logical operations are substantially the same. 
   
   
     17. The method of  claim 14 , wherein the step of changing the level of the first detection signal comprises:
 setting the level of the first detection signal to a first predetermined level during the active period of the first control signal. 
 
   
   
     18. The method of  claim 17 , wherein the step of changing the level of the second detection signal comprises:
 setting the level of the second detection signal to the first predetermined level during the active period of the second control signal. 
 
   
   
     19. The method of  claim 14 , wherein the step of changing the level of the first output signal comprises:
 setting the level of the first output signal to a first predetermined level during the active period of the third control signal. 
 
   
   
     20. The method of  claim 19 , wherein the step of changing the level of the second output signal comprises:
 setting the level of the second output signal to the first predetermined level during the active period of the third control signal. 
 
   
   
     21. A signal generating module comprising:
 a first latch unit for latching a first input signal to generate a first latched signal and for changing the level of the first latched signal according to a control signal; 
 a first delay unit coupled to the first latching unit for delaying the first latched signal to generate a first delayed signal; 
 a second latch unit for latching a second input signal to generate a second latched signal and for changing the level of the second latched signal according to the control signal; 
 a second delay unit coupled to the second latching unit for delaying the second latched signal to generate a second delayed signal; 
 a combination logic coupled to the first and second latch units for performing a predetermined logical operation on the first latched signal and the second latched signal to generate the control signal; 
 a first logic unit, coupled to the first delay unit and the combination logic, for performing a first logical operation on the first delayed signal and the control signal to generate a first signal; and 
 a second logic unit, coupled to the second delay unit and the combination logic, for performing a second logical operation on the second delayed signal and the control signal to generate a second signal. 
 
   
   
     22. A signal generation method comprising:
 latching a first input signal to generate a first latched signal; 
 changing the level of the first latched signal according to a control signal; 
 delaying the first latched signal to generate a first delayed signal; 
 latching a second input signal to generate a second latched signal; 
 changing the level of the second latched signal according to the control signal; 
 delaying the second latched signal to generate a second delayed signal; 
 performing a predetermined logical operation on the first latched signal and the second latched signal to generate the control signal; 
 performing a first logical operation on the first delayed signal and the control signal to generate a first signal; and 
 performing a second logical operation on the second delayed signal and the control signal to generate a second signal.